1. Field of the Invention
The present invention is directed generally to monitoring operating parameters in a steam turbine generator and, more specifically, to the monitoring of the clearance between the turbine shroud and the turbine seal.
2. Cross Reference to Related Application
The present application is related to U.S. application Ser. No. 201,225 entitled SHROUDED TURBINE BLADE VIBRATION MONITOR filed 6/2/88, which is assigned to the same assignee as the present invention (W.E. 54,116).
3. Description of the Prior Art
Apparatus exist for measuring various operating parameters in steam turbine generators. One such apparatus is disclosed in U.S. Pat. No. 4,644,270 wherein a plurality of proximity sensors measure steam flow guide to turbine blade top distance at various points around a flow guide. However, such an apparatus is not easily adaptable to a shrouded turbine blade arrangement.
A typical prior art shrouded turbine blade row 10 (FIG. 1) includes the following components: rotor disk 11, blades 12, shroud segments 13, tenons 14 and seal 15. The tenons 14 are integral parts of the blades 12 that serve to fasten the shroud segments 13 to the blades 12. The seal 15 reduces the amount of steam that passes around instead of through the turbine blades 12.
The clearance between the seal 15 and the shroud segments 13 must not be so great as to allow an excessive amount of steam to pass between them and thereby reduce the efficiency of the turbine. On the other hand, any contact between the shroud segments 13 and the seal 15 will result in both components being destroyed. Because of the dynamic nature of a steam turbine and the forces and temperatures involved, the clearance between the shroud segments 13 and the seal 15 varies during operation. Therefore, it is desirable to monitor this clearance on a real-time basis in order to prevent damage to the rotating machinery.
In an attempt to reduce the number of unscheduled outages in steam turbine generator systems and protect the integrity of the components of the turbine generator, use is made of monitoring systems which detect and alert operators of abnormal operating conditions. However, because of the physical differences between shrouded and unshrouded turbine blades, monitoring systems used on the latter are not easily adaptable for use on the former. Accordingly, a device is needed that will indicate when the clearance between the shroud segments 13 and seal 15 is approaching a minimum limit established by the risk of contact. The present invention fills the need for a turbine blade shroud clearance monitoring system.